Group III-V films are finding greater importance in the development and fabrication of a variety of semiconductor devices, such as short wavelength light emitting diodes (LEDs), laser diodes (LDs), and electronic devices including high power, high frequency, high temperature transistors and integrated circuits. For example, short wavelength (e.g., blue/green to ultraviolet) LEDs are fabricated using the Group III-nitride semiconducting material gallium nitride (GaN). It has been observed that short wavelength LEDs fabricated using GaN can provide significantly greater efficiencies and longer operating lifetimes than short wavelength LEDs fabricated using non-nitride semiconducting materials, such as Group II-VI materials.
One method that has been used for depositing Group III-nitrides, such as GaN, is metal organic chemical vapor deposition (MOCVD). This chemical vapor deposition method is generally performed in a reactor having a temperature controlled environment to assure the stability of a first precursor gas which contains at least one element from Group III, such as gallium (Ga). A second precursor gas, such as ammonia (NH3), provides the nitrogen needed to form a Group III-nitride. The two precursor gases are injected into a processing zone within the reactor where they mix and move towards a heated substrate in the processing zone. A carrier gas may be used to assist in the transport of the precursor gases towards the substrate. The precursors react at the surface of the heated substrate to form a Group III-nitride layer, such as GaN, on the substrate surface. The quality of the film depends in part upon deposition uniformity which, in turn, depends upon uniform mixing of the precursors across the substrate.
To accomplish deposition of the layer on substrates, multiple substrates may be arranged on a substrate carrier and each substrate may have a diameter ranging from 50 mm to 100 mm or larger. The uniform mixing of precursors over larger substrates and/or more substrates and larger deposition areas is desirable in order to increase yield and throughput. These factors are important since they directly affect the cost to produce an electronic device and, thus, a device manufacturer's competitiveness in the market place.
The different gases, which when combined react to form the deposition layer, are generally provided through different pathways in a gas distributor to the reaction chamber. As the gases exit the gas distributor, they mix and begin reacting. Generally, the gas distributor is kept at a temperature well below the substrate temperature to avoid decomposition of gases in the precursor pathways before the precursor gases reach the substrate. Although most reaction products are formed near the heated substrate, some begin forming as the precursors mix near the exit of the gas distributor, and condense and deposit on the gas distributor. The deposits build up over many deposition cycles, until there is an unacceptable risk that particles formed from this unwanted deposition will dislodge during deposition and contaminate substrates being processed in the chamber. Thus, there is a need for methods and apparatus to prevent or retard buildup of such deposits.